In hermetic compressors of the reciprocating type and with little displacement volume (small cylinder capacity), both suction and discharge valves exert a strong influence on the compressor performance.
The valve plate and valve blade assemblies that form the valve systems as a whole, act directly on the energy and mass efficiency of the compressor.
Energy losses in the compressor are basically characterized by the resistance of the valve to open readily and by the restriction of flow during the admission or discharge of gas. Such losses are directly related to the speed and readiness of the blades to move to the valve opening position.
The predominant factors contributing to the occurrence of said losses, mainly those caused by the delay in the opening of the blades, are the following:
inadequate shape of geometry of the gas orifice and/or the valve seat, preventing the valve from having a maximum effective force area for the initial opening of the blade;
blade inertia, caused by blade overweight (mass) and/or inadequate geometry; and
blade adhering sticking to the valve plate due to the presence of viscous lubricant oil.
When these factors occur in the suction valve, they exert strong influence on the volumetric efficiency of the compressor. In the case of the discharge valve, the losses are basically energetic, i.e. overpressure losses to impel the blade to initiate its opening.
The types of valve systems that are normally used and/or proposed nowadays are of the type described in U.S. Pat. Nos. 4,642,037 and 4,580,604. In these prior art valve systems, the only object of the invention is to minimize the delay in the opening of the blade by reducing the adherence (sticktion or sticking) effect caused by the viscosity of the lubricant oil.
However, another problem of fundamental importance is still unsolved, i.e. to minimize the inertia effect of the blade, mainly at the initial moment of the valve opening. The reduction of the weight (mass) of the blade and, consequently, of its inertia, taking into account the materials available nowadays, is more efficiently obtained by reducing the blade thickness. However, this can lead to excessively high strain on the blade, mainly on the region over the orifice. As a result, it would be necessary to reduce the diameter of the orifice, thereby reducing the effective force and flow areas and consequently the performance of the compressor.
It should also be understood that, although the suction and discharge valves operate under rather different conditions, the above mentioned aspects are common for both valves.